Finally it would be interesting to know whether the index structure computed in
linear time for the enumeration process could be updated efficiently. In the
boolean case, queries of arity 0, updates can be done in constant
time [1]}, assuming the underlying graph is not changed too
much. In particular a relabeling of a node require only constant update
time. It would be interesting to know whether this constant update time could
also be achieved for an index structure allowing for constant delay
enumeration.
